The invention relates to a failsafe emergency operation device for idling operation in motor vehicles, in particular for a digital idling charge regulation means. The device includes a final control element (two-coil rotary adjuster) which acts as an air bypass parallel to the throttle valve and is triggered by an end stage circuit.
For controlling electrical or electromechanical equipment or for controlling system functions, it is known to use microprocessors or microcomputers which derive control signals for the actuation of final control elements from one or more operating parameters of the system. Such devices are used in motor vehicles, for instance to operate injection systems, ignition systems, transmission controls or an idling charge regulating means, either separately or combined in a central logic block. In this context, it is also known to provide monitoring devices, which monitor the proper operation of the equipment and emit an alarm signal and/or effect emergency control if a malfunction occurs.
SAE Technical Paper No. 810157 describes a microcomputer-controlled means of regulating an internal combustion engine. The microcomputer or microprocessor used there generates control pulses which are built into its control program; these pulses are completed by the microprocessor and therefore appear at regular intervals when the equipment is functioning properly. A malfunction in the program or on the part of the device can then be detected by a memory circuit or some other device, since in this case--for instance if the computer shuts down--no further control pulses are emitted. In the monitoring circuit according to this SAE Paper, a monostable multivibrator is provided, the output of which can be supplied to the injection system and the ignition device. Below a prescribed engine speed, the regular control pulses are suppressed; this is the case particularly when the engine is started.
A reset circuit for a microcomputer is also known from German Offenlegungsschrift No. 30 35 896, in which the control pulses indirectly effect the charging or discharging of a capacitor, so that the absence of the control pulses can be recognized by monitoring the capacitor voltage. If changes beyond a predetermined extent occur in the sequence of the control pulses, then the monitoring circuit generates a reset signal which resets the microcomputer. The reset phase is then followed by an unblocking phase, in which the system can start up once again.
Problems can arise in the known devices for monitoring system functions whenever a function has to be monitored which is critical to safety in the event of an undefined malfunction; an example, with an idling charge regulating means, would be the possibility that a two-coil rotary adjuster used for this type of regulation might assume a position corresponding to an undesirable acceleration.
The need therefore exists for a monitoring circuit for use with an idling charge regulating means, which is capable of assuring that in the case of some malfunction the idling charge regulating means will behave in a clearly defined manner and without critically affecting safety.